Post-grouting, or tip or base grouting, refers to a variety of practices related to injection of grout under pressure below the tip of a drilled shaft foundation to improve the stiffness and nominal resistance of a shaft to top-down loading when subjected to compressive axial load. The grout may be neat cement grout (i.e., Portland cement and water). Post-grouting may be accomplished using a grout delivery system that is incorporated into a drilled shaft during construction. The grout delivery system generally includes one or more tubes or pipes that pass from the top of the shaft to a grout distribution apparatus located at the tip of the shaft. When adequately instrumented and properly monitored, the post-grouting process is believed to provide increased reliability compared to conventional (ungrouted) drilled shafts, since the process provides a measurable indication of performance.
Post-grouting requires delivery of grout material after the drilled shaft foundation has been installed. Pipes that run the length of the drilled shaft that are used to deliver the grout material are added and permanently remain part of the completed shaft. Providing the additional pipes is an additional expense that adds to undesirable congestion of the steel reinforcement cage used for the drilled shaft foundation. Furthermore, once post-grouting is complete, the pipes used for post-grouting provide no structural contribution to the drilled shaft foundation and thus are a relatively inefficient component thereof.
Accordingly, it is desirable to provide a more efficient mechanism for using a post-grout delivery system of a drilled shaft foundation.